This invention relates to a high-performance and high-reliability magnetic recording medium, a method thereof, and a magnetic recording unit using thereof.
Japanese Laid-open Patent Publication No. 10-177712 (1998) has disclosed a magnetic recording medium comprising a glass substrate, a first under layer comprising tantalum (Ta) and boron (B), a second under layer mainly comprising chromium (Cr), and a magnetic layer which are laminated on said substrate; wherein said first under layer works to adjust sizes of grains in the second ground and magnetic layers, and said ground and magnetic layers are formed with the fine crystals of said first under layer directly reflected upon them. This invention is characterized by high coercive force and low noises.
Japanese Laid-open Patent Publication No. 6-259743 (1994) has disclosed a magnetic recording medium comprising a non-magnetic substrate, a second under layer having sodium chloride (NaCl) type crystal structure, a first under layer having a body-centered cubic structure, and a magnetic layer having a hexagonal close-packed structure which are laminated on said substrate. This invention is characterized by improved crystal orientation of the magnetic layers.
Japanese Laid-open Patent Publication No. 7-311929 (1995) has disclosed a magnetic recording medium having a thin magnetic layer on a NiP under layer wherein crystal particles in said magnetic layer are isolated from each other by a crystal grain boundary containing non-ferromagnetic non-metallic phase. This invention is characterized by high coercive force and low noises.
Japanese Laid-open Patent Publication No. 11-66533 (1999) has disclosed a magnetic recording medium forming a thin magnetic layer on a non-magnetic under layer made of one or more of metals Cr, Pt, Ta, Ni, Ti, Ag, Cu, Al, Au, W, Mo, Nb, V, Zr, and Zn; wherein lots of magnetic particles in said magnetic layer are isolated from each other by grain boundary comprising the same components as the magnetic particles. This invention is characterized by high coercive force and low noises.
However, the aforesaid conventional technologies have limitations on control of distributions of sizes of crystal particles in a magnetic layer constituting the magnetic recording disk medium. Therefore, the magnetic layer cannot be free from containing both fine and large particles. Information recorded on such magnetic layers would be affected and disturbed by magnetic fields (noises) leaking from surrounding larger particles or mutual actions of large particles. Such noises are enemies to super-high density recording of 20 Gbit/inch2 or above.
One object of the present invention is to provide a magnetic recording medium fit for stable high-density recording and a method thereof.
Another object of the present invention is to provide a magnetic recording unit using said magnetic recording medium.
We inventors discovered that the size and distribution (or uniformity of grain size) of crystal particles in an inorganic compound layer are very dependent upon the size and distribution of a magnetic film by growing the magnetic film on the inorganic compound layer which comprises crystal particles and amorphous grain phase surrounding the crystal particles.
Further, we discovered that we could obtain a stable high-density recording magnetic film having fine magnetic particles of almost an identical size arranged regularly by narrowing the grain size distribution of the crystal particles in the inorganic compound layer, that is, controlling to have fine and uniform size of the crystal particles in the inorganic compound layer.
Further, we discovered that, for a magnetic layer comprising crystal magnetic particles and deposits (a grain boundary phase) formed around the magnetic particles, the magnetic particles of the magnetic layer are finer and their grain sizes are uniform.
Furthermore, an intermediate layer can be provided between the inorganic compound layer and the magnetic layer. We discovered that we could control the particular structure of the magnetic layer by controlling the size and distribution of the crystal particles of the intermediate layer. Particularly, when a magnetic layer comprises crystal magnetic particles and deposits (a grain boundary phase) formed around the magnetic particles, we discovered that the magnetic particles of the magnetic layer were finer and their grain sizes were uniform. Below will be explained the summary of the present invention.
(1) A magnetic recording medium comprising a substrate and a plurality of information-recording magnetic layers laminated on said substrate, further comprising an inorganic compound layer containing crystal particles and amorphous grain boundary phases surrounding said particles between said substrate and said magnetic layers; wherein
said magnetic layers contains crystal magnetic particles whose mean grain size is 4 nm to 15 nm and the standard deviation of the grain size ("sgr") is 25% or less of said mean grain size.
(2) Said magnetic layers are on said magnetic recording medium comprising crystal magnetic particles and an amorphous grain boundary phase surrounding said magnetic particles.
(3) Said inorganic compound layer comprises a first component containing sodium chloride (NaCl) or spinel type crystal oxide and a second component containing oxide, nitride, or boride of elements belonging to Groups I to V of the periodic table. Said particles and said grain boundary phase contain both the first and second components and said particles contain more first component than said grain boundary phase.
The inorganic compound layer fit for the magnetic recording medium according to the present invention contains
(a) a first component comprising sodium chloride (NaCl) or spinel type crystal oxide and
(b) a second component comprising at least one of oxide, nitride, and boride of elements belonging to Groups I to V of the periodic table.
An oxide having the sodium chloride (NaCl) type crystal structure can be one selected from a group of cobalt oxide (CoO), ferric oxide (Fe2O3), magnesium oxide, manganese oxide, titanium oxide, copper oxide or nickel oxide.
Similarly, a spinel type crystal oxide can be selected from cobalt oxide (Co3O4) or ferrous oxide (Fe3O4).
Said crystal particle of the inorganic compound layer contains 65% to 98% by weight of oxide (a) and 35% to 2% by weight of oxide (b) and said grain boundary phase contains 50% to 90% by weight of oxide (a) and 50% to 10% by weight of oxide (b). Both the crystal particles and the grain bound a ryphase preferentially contain oxides (a) and (b). Further, the crystal particle of the inorganic compound layer should always contain greater oxide (a) than the grain boundary phase. Here, the mean grain size, the standard deviation ("sgr") of grain size, the short diameter to long diameter ratio of said particle, and the grain boundary phase width should be respectively 4 nm to 15 nm, 25% or less of said mean grain size, 0.7 to 1.0 and 0.1 nm to 2 nm in that order.
The magnetic layer formed on the inorganic compound layer is a ferromagnetic layer which is an alloy of cobalt (Co) as a main component, platinum (Pt), and at least one selected from a group of elements chrome (Cr), tantalum (Ta), and niobium (Nb). This ferromagnetic layer has a structure in which at least one of chrome (Cr), tantalum (Ta), and niobium (Nb) is deposited between the crystal particles mainly comprising cobalt (Co) and other crystal particles.
The sizes and size distribution of magnetic particles in the magnetic layer are approximately equal to those of the inorganic compound layer due to the particle structure of the inorganic compound layer reflecting the magnetic particles in the magnetic layer. Therefore, the magnetic layer can have fine magnetic particles of uniform size.
At least one of oxide, nitride, and boride of elements belonging to Groups I to V of the periodic table can be deposited on the boundary of the magnetic particles. In this case, the sizes and size distribution of magnetic particles in the magnetic layer are approximately equal to those of the inorganic compound layer. The mean grain size, the short diameter to long diameter ratio of said particle, and the standard deviation ("sgr") of grain size are respectively 4 nm to 15 nm, 0.7 to 1.0, and 25% or less of said mean grain size in that order.
If the difference between lattice constants of the crystal of the magnetic particles of the magnetic layer and the particles of the inorganic compound layer is xc2x110% or under, the sizes and size distribution of magnetic particles in the magnetic layer become closer to those of the inorganic compound layer.
The intermediate layer between the inorganic compound layer and the magnetic layer uses a chrome-related metal layer. The sizes and size distribution of metal particles in the intermediate layer reflect the particle structure of the inorganic compound layer and the sizes and size distribution of magnetic particles in magnetic layer reflect the particle structure of metal particles of the inorganic compound layer. In other words, the sizes and size distribution of magnetic particles in the magnetic layer are approximately equal to those of the inorganic compound layer and we can obtain a magnetic layer of fine particles of uniform sizes.
At least one of oxide, nitride, and boride of elements belonging to Groups I to V of the periodic table can be deposited on the boundary of the Cr-related metal particles of the intermediate layer. In this case, the sizes and size distribution of magnetic particles in the magnetic layer becomes closer to those of the inorganic compound layer.